Ballistic resistant body armor articles

ABSTRACT

The present invention relates to body armor articles for resisting ballistic objects. The articles comprise unidirectional fabric layers and sheet layers. The unidirectional fabric layers are made from yarns having a tenacity of at least 7.3 grams per dtex and a modulus of at least 100 grams per dtex. The sheet layers comprise non-woven random oriented fibrous sheets and/or non-fibrous films. The unidirectional fabric layers and the sheet layers are stacked together comprising a first core section which includes at least two repeating units of, in order, at least one of the unidirectional fabric layers then at least one of the sheet layers. The sheet layers comprise 0.5 to 30 wt % of the total weight of the article.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to ballistic resistant body armor.

2. Description of Related Art

Many designs for body armor for resisting ballistic threats have been proposed and many commercialized. Designs are made to increase comfort by the wearer to increase their use. Comfort is generally increased by making them lighter and more flexible to allow freedom of motion by the wearer. However, apparel weight needs to be increased to provide protection against projectiles with greater velocities and mass. It is also desirable to minimize the costs to make the apparel, but traditional materials used in body armor are relatively expensive.

Standards have been proposed and adopted throughout the world to ensure minimum capabilities of body armor for resisting ballistic objects. See NIJ Standard—0101.06 “Ballistic Resistance of Body Armor”, issued in July 2008. It defines capabilities for body armor for level IIA, II, IIIA and III protection. To achieve level II protection, the armor must have no penetration and no more than a backface deformation of 44 mm by a projectile such as a 0.357 magnum projectile at a velocity (V_(o)) defined as 1430 ft/sec plus or minus (+/−) 30 feet per sec (436 m/sec+/−9 m/sec). To achieve level IIIA protection, the armor must have no penetration and no more than a backface deformation of 44 mm by a projectile such as a 0.44 magnum projectile at a velocity (V_(o)) defined as 1430 ft/sec plus or minus (+/−) 30 feet per sec (436 m/sec+/−9 m/sec). Body armor is frequently designed with a margin of safety surpassing the requirements of the Standard. However, increasing the margin of safety typically increases the cost and weight and decreases the flexibility of the body armor. So body armor is typically made to meet published standards with a small margin of safety, but not much more.

There are also many designs for body armor for resisting spike (e.g., ice pick like) or knife stabbing or slashing threats. However, such designs typically are not optimum or even necessarily able to protect against ballistic threats. Separate standards have been published providing different tests and requirements for such spike or knife resistant body armor compared to standards for ballistic resistant body armor. Thus, those skilled in the art do not assume teachings on making or optimizing spike or knife resistant body armor to be useful in designing ballistic resistant body armor.

Many body armor products meeting the NIJ ballistic standard level II or IIIA protection can be made solely of woven fabric layers made from high tenacity multifilament yarns, such as made from para-aramid. Such woven fabric layers provide very good penetration resistance against bullets and fragments. However, woven fabric layers alone provide less protection against backface deformation requiring more layers and increased weight to meet the margin of safety or even the standard. Hybrid body armor meeting the level II or IIIA protection can be made using a plurality of such woven fabric layers stacked in combination with a plurality of unidirectional assemblies comprising a unidirectional tape made of an array of parallel high tenacity multifilament yarns in a matrix resin stacked with adjacent tapes with their yarns at angles inclined with respect to adjacent tapes. Typically the yarns in the tapes are at right angles with respect to yarns in adjacent tapes. These hybrid body armors provide good penetration resistance against bullets, greater protection against backface deformation, but replacing woven fabric layers with unidirectional assemblies increases rigidity and increases cost. Body armor meeting the level II or IIIA protection can be made solely using a plurality of the unidirectional assemblies. They provide good penetration resistance against bullets, very good protection against backface deformation, but they typically are more rigid than the other options, and are the most expensive.

There remains a need however to provide a flexible antiballistic article at a lower weight and cost that is effective against hand gun bullets. Unidirectional fabrics can provide a platform for such an article.

U.S. Pat. No. 8,015,617 to Carabajal et al describes body armor articles comprising woven fabric layers and sheet layers. The woven fabric layers are made from yarns having a tenacity of at least 7.3 grams per dtex and a modulus of at least 100 grams per dtex. The sheet layers comprise non-woven random oriented fibrous sheets and/or non fibrous films. The woven fabric layers and the sheet layers are stacked together comprising a first core section which includes at least two repeating units of, in order, at least one of the woven fabric layers then at least one of the sheet layers. The sheet layers have an acoustic velocity of at least 600 m/sec and comprise from 0.5 to 30 wt % of the total weight of the article.

BRIEF SUMMARY OF THE INVENTION

The invention relates to body armor articles for resisting ballistic objects, comprising a plurality of unidirectional fabric layers made from yarns having a tenacity of at least 7.3 grams per dtex and a modulus of at least 100 grams per dtex; a plurality of sheet layers comprising non-woven random oriented fibrous sheets and/or non-fibrous films, each of the sheet layers having a thickness of at least 0.013 mm; the unidirectional fabric layers and the sheet layers stacked together comprising a first core section which includes at least two repeating units of, in order, at least one of the unidirectional fabric layers then at least one of the sheet layers; wherein

(i) the sheet layers comprise 0.5 to 30 wt % of the total weight of the article,

(ii) each of the sheet layers has an average acoustic velocity at least 600 m/sec,

(iii) the sheet layers are isotropic or substantially isotropic for average acoustic velocity, and

(iv) the unidirectional fabric layers and the sheet layers are attached together at 10% or less of their surface areas.

BRIEF DESCRIPTION OF THE DRAWING

The invention can be more fully understood from the following detailed description thereof in connection with accompanying drawings described as follows.

FIG. 1 is an exploded perspective view of a first embodiment of a ballistic penetration resistant article with a sheet layer on one end and a unidirectional fabric layer on the other end in accordance with the present invention.

FIG. 2 is an exploded perspective view of a repeating section having, in order, a plurality of sheet layers and a plurality of unidirectional fabric layers in accordance with the present invention.

FIG. 3 is an exploded perspective view of a second embodiment of a ballistic penetration resistant article with a unidirectional fabric layer on each end in accordance with the present invention.

FIG. 4 is an exploded perspective view of a third embodiment of a ballistic penetration resistant article comprising, in order, a first strike section, a repeating section, and a body facing section in accordance with the present invention.

FIG. 5 is a an exploded perspective view of a fourth embodiment of a ballistic penetration article comprising, in order, a first strike section, a first repeating section, a second repeating section, and a body section in accordance with the present invention.

FIG. 6 shows a first manner for attaching layers together.

FIG. 7 shows a second manner for attaching layers together.

FIG. 8 shows a third manner for attaching layers together.

FIG. 9 is an exploded perspective view of another embodiment of a ballistic penetration article comprising, in order, a plurality of auxiliary fabric layers, a core section, and a plurality of auxiliary fabric layers.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to the following detailed description of illustrative and preferred embodiments that form a part of this disclosure. It is to be understood that the scope of the claims is not limited to the specific devices, methods, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the claimed invention. Also, as used in the specification including the appended claims, the singular forms “a,” “an,” and “the” include the plural, and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. When a range of values is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. All descriptions, limitations and ranges are inclusive and combinable. Further, throughout the following detailed description, similar reference characters refer to similar elements in all figures of the drawings.

Referring to FIG. 1 which shows an exploded perspective view of one embodiment of the present invention, the invention is directed to a body armor article 10 for resisting ballistic objects. The body armor article 10 is for incorporation into body armor and comprises a plurality of unidirectional fabric layers 12 and a plurality of sheet layers 14 stacked together to comprise a first core section 16. The first core section 16 includes at least two repeating units 22 of, in order, at least one of the unidirectional fabric layers 12 then at least one of the sheet layers 14. The sheet layers 14 comprise 0.5 to 30 wt % of the total weight of the article.

Unidirectional Fabric Layers

The fabric layers 12 are unidirectional. The term “unidirectional” is meant herein to be any fabric comprising yarns in which all the yarns within a layer of the fabric lie parallel to each other. In a fabric comprising a plurality of layers, the orientation of yarns in one layer is different from the orientation of yarns in an adjacent layer.

The unidirectional fabric is substantially coated with a matrix resin. The coating may be on the surface of the yarns comprising the fabric or between the filaments of a yarn or both. By “matrix resin” is meant an essentially homogeneous resin or polymer material in which the yarn is embedded. The matrix resin may be a thermoplastic or thermoset resin.

In some embodiments, each unidirectional fabric layer 12 has a basis weight of from 50 to 800 g/m². In some preferred embodiments the basis weight of each unidirectional layer is from 70 to 600 g/m². In some most preferred embodiments the basis weight of a unidirectional layer is from 90 to 500 g/m².

Yarns and Filaments

The unidirectional fabric layers 12 are made from multifilament yarns having a plurality of filaments. The yarns can be intertwined and/or twisted. For purposes herein, the term “filament” is defined as a relatively flexible, macroscopically homogeneous body having a high ratio of length to width across its cross-sectional area perpendicular to its length. The filament cross section can be any shape, but is typically circular or bean shaped. Herein, the term “fiber” is used interchangeably with the term “filament”, and the term “end” is used interchangeably with the term “yarn”.

The filaments can be any length. Preferably the filaments are continuous. Multifilament yarn spun onto a bobbin in a package contains a plurality of continuous filaments. The multifilament yarn can be cut into staple fibers and made into a spun staple yarn suitable for use in the present invention. The staple fiber can have a length of about 1.5 to about 5 inches (about 3.8 cm to about 12.7 cm). The staple fiber can be straight (i.e., non crimped) or crimped to have a saw tooth shaped crimp along its length, with a crimp (or repeating bend) frequency of about 3.5 to about 18 crimps per inch (about 1.4 to about 7.1 crimps per cm).

The yarns have a yarn tenacity of at least 7.3 grams per dtex and a modulus of at least 100 grams per dtex. Preferably, the yarns have a linear density of 50 to 4500 dtex, a tenacity of 10 to 65 g/dtex, a modulus of 150 to 2700 g/dtex, and an elongation to break of 1 to 8 percent. More preferably, the yarns have a linear density of 100 to 3500 dtex, a tenacity of 15 to 50 g/dtex, a modulus of 200 to 2200 g/dtex, and an elongation to break of 1.5 to 6 percent.

Fabric Layer Fiber Polymer

The yarns of the present invention may be made with filaments made from any polymer that produces a high-strength fiber, including, for example, polyamides, polyolefins, polyazoles, and mixtures of these.

When the polymer is polyamide, aramid is preferred. The term “aramid” means a polyamide wherein at least 85% of the amide (—CONH—) linkages are attached directly to two aromatic rings. Suitable aramid fibers are described in Man-Made Fibres—Science and Technology, Volume 2, Section titled Fibre-Forming Aromatic Polyamides, page 297, W. Black et al., Interscience Publishers, 1968. Aramid fibers and their production are, also, disclosed in U.S. Pat. Nos. 3,767,756; 4,172,938; 3,869,429; 3,869,430; 3,819,587; 3,673,143; 3,354,127; and 3,094,511.

The preferred aramid is a para-aramid. The preferred para-aramid is poly(p-phenylene terephthalamide) which is called PPD-T. By PPD-T is meant the homopolymer resulting from mole-for-mole polymerization of p-phenylene diamine and terephthaloyl chloride and, also, copolymers resulting from incorporation of small amounts of other diamines with the p-phenylene diamine and of small amounts of other diacid chlorides with the terephthaloyl chloride. As a general rule, other diamines and other diacid chlorides can be used in amounts up to as much as about 10 mole percent of the p-phenylene diamine or the terephthaloyl chloride, or perhaps slightly higher, provided only that the other diamines and diacid chlorides have no reactive groups which interfere with the polymerization reaction. PPD-T, also, means copolymers resulting from incorporation of other aromatic diamines and other aromatic diacid chlorides such as, for example, 2,6-naphthaloyl chloride or chloro- or dichloroterephthaloyl chloride or 3,4′-diaminodiphenylether.

Additives can be used with the aramid and it has been found that up to as much as 10 percent or more, by weight, of other polymeric material can be blended with the aramid. Copolymers can be used having as much as 10 percent or more of other diamine substituted for the diamine of the aramid or as much as 10 percent or more of other diacid chloride substituted for the diacid chloride or the aramid.

When the polymer is polyolefin, polyethylene or polypropylene is preferred. The term “polyethylene” means a predominantly linear polyethylene material of preferably more than one million molecular weight that may contain minor amounts of chain branching or comonomers not exceeding 5 modifying units per 100 main chain carbon atoms, and that may also contain admixed therewith not more than about 50 weight percent of one or more polymeric additives such as alkene-1-polymers, in particular low density polyethylene, propylene, and the like, or low molecular weight additives such as anti-oxidants, lubricants, ultra-violet screening agents, colorants and the like which are commonly incorporated. Such is commonly known as extended chain polyethylene (ECPE) or ultra high molecular weight polyethylene (UHMWPE). Preparation of polyethylene fibers is discussed in U.S. Pat. Nos. 4,478,083, 4,228,118, 4,276,348 and Japanese Patents 60-047,922, 64-008,732. High molecular weight linear polyolefin fibers are commercially available. Preparation of polyolefin fibers is discussed in U.S. Pat. No. 4,457,985.

In some preferred embodiments polyazoles are polyarenazoles such as polybenzazoles and polypyridazoles. Suitable polyazoles include homopolymers and, also, copolymers. Additives can be used with the polyazoles and up to as much as 10 percent, by weight, of other polymeric material can be blended with the polyazoles. Also copolymers can be used having as much as 10 percent or more of other monomer substituted for a monomer of the polyazoles. Suitable polyazole homopolymers and copolymers can be made by known procedures, such as those described in or derived from U.S. Pat. No. 4,533,693 (to Wolfe, et al., on Aug. 6, 1985), U.S. Pat. No. 4,703,103 (to Wolfe, et al., on Oct. 27, 1987), U.S. Pat. No. 5,089,591 (to Gregory, et al., on Feb. 18, 1992), U.S. Pat. No. 4,772,678 (Sybert, et al., on Sep. 20, 1988), U.S. Pat. No. 4,847,350 (to Harris, et al., on Aug. 11, 1992), and U.S. Pat. No. 5,276,128 (to Rosenberg, et al., on Jan. 4, 1994).

Preferred polybenzazoles are polybenzimidazoles, polybenzothiazoles, and polybenzoxazoles and more preferably such polymers that can form fibers having yarn tenacities of 30 gpd or greater. If the polybenzazole is a polybenzothioazole, preferably it is poly(p-phenylene benzobisthiazole). If the polybenzazole is a polybenzoxazole, preferably it is a it is poly(p-phenylene benzobisoxazole) and more preferably the poly(p-phenylene-2,6-benzobisoxazole) called PBO.

Preferred polypyridazoles are polypyridimidazoles, polypyridothiazoles, and polypyridoxazoles and more preferably such polymers that can form fibers having yarn tenacities of 30 gpd or greater. In some embodiments, the preferred polypyridazole is a polypyridobisazole. The preferred poly(pyridobisozazole) is poly(1,4-(2,5-dihydroxy)phenylene-2,6-pyrido[2,3-d:5,6-d′]bisimidazole which is called PIPD. Suitable polypyridazoles, including polypyridobisazoles, can be made by known procedures, such as those described in U.S. Pat. No. 5,674,969.

Sheet Layers

The sheet layers 14 comprise non-woven random oriented fibrous sheets and/or non fibrous films.

By “non-woven random oriented fibrous sheet” is meant a unitary network or arrangement of fibers that are not “woven” together. The non-woven random oriented fibrous sheets are made of random oriented fibers. Suitable examples of non-woven random oriented fibrous sheets include spun bonded fibrous webs, felt, fiber batts, and the like. The fibers in the non-woven random oriented fibrous sheets can be made from any polymer that produces a fiber that can be laid down in a random fashion in sheet form including, for example, polyamides, polyolefins, polyazoles, and mixtures of these. Spunbonded fibrous webs can be formed by filaments that have been extruded, drawn, and then laid on a continuous belt. Bonding can be accomplished by several methods such as by hot roll calendering or by passing the web through a saturated stream chamber at en elevated pressure. Preferably, the non-woven random oriented fibrous sheets are spunbonded fibrous webs. A preferred spunbonded fibrous web is Tyvek® brand high density polyethylene sheets made by E. I. du Pont de Nemours and Company with offices in Wilmington, Del., U.S.A.

Other fibers suitable for use in a non-woven randomly oriented fibrous matt or veil are aramid, glass, ceramic and carbon. Such materials are available under the tradename Optimat from Technical Fiber Products Inc., Schenectady, N.Y. or from Hollingsworth and Vose, East Walpole, Mass. Highly fibrillated fibers such as aramid micropulp from E. I. DuPont de Nemours and Company, Wilmington, Del. can be used. Other fiber forms include those having a filament diameter of less than one miocrometer.

By “non fibrous film” is meant a continuous flexible polymeric film or sheet produced by methods such as extrusion, coextrusion and casting that is free of fibrous filaments. The non fibrous film may be made of polycondensation products of dicarboxylic acids with dihydroxyalcohols such as polyester, ionomers, thermoplastic fluoropolymers, polyolefins, polyimides and mixtures thereof. Suitable polyesters include saturated polyesters such as polyethylene terephthalate, polycarbonate and polybutyrate. One useful polyethylene terephthalate is available under the tradename Mylar®. A suitable ionomer is ethylene methacrylic acid copolymer; one suitable ionomer is available under the tradename Surlyn®. Examples of fluoroploymers include polyvinyl fluoride, poly(tetrafluoroethylene), polyvinyl chloride and polyvinylidene fluoride. A suitable polyvinyl fluoride material is available under the tradename Tedlar®. Suitable polyolefins include polyethylene and polypropylene. Suitable polyimides are aromatic heterocyclic polyimides and linear polyimides such as those available under the tradenames Kapton®, Apical® and Kaptrex®.

Each of the sheet layers 14 have a thickness of at least 0.013 mm (0.5 mils). Preferably, each of the sheet layers 14 has a thickness of no more than 0.152 mm (6 mils). More preferably, each of the sheet layers 14 has a thickness of 0.015 to 0.142 mm.

In some embodiments, the sheet layers are isotropic or substantially isotropic with respect to one or more properties of the sheet layers (such as average acoustic velocity). By “substantially isotropic” it is meant that the sheet layers have substantial uniformity with respect to a selected property (such as acoustic velocity) measured in at least two directions or orientations. For example, the property being measured may vary by less than about 25%, less than about 20%, or even vary by less than 10% in at least two directions.

Preferably, the sheet layers 14 are made of materials with an average acoustic velocity of at least 600 m/sec, more preferably at least 700 m/sec and even more preferably at least 1500 m/sec.

Each of the sheet layers 14 has a ratio of maximum strain to failure value to minimum strain to failure value of 1 to 5, preferably 1 to 3, when tested in accordance with ASTM method D882.

The sheet layers 14 comprise 0.5 to 30 wt %, more preferably 3 to 28 wt %, and even more preferably 5 to 26 wt %, of the total weight of the article 10, 26, 40, 48.

Core Section

The unidirectional fabric layers 12 and the sheet layers 14 stacked together comprise the first core section 16. The first core section 16 preferably includes 3 to 60 of the unidirectional fabric layers 12 and 3 to 60 of the sheet layers 14. More preferably, it includes 8 to 50 of the unidirectional fabric layers 12 and 5 to 50 of the sheet layers 14. Even more preferably, it includes 10 to 45 of the unidirectional fabric layers 12 and 8 to 45 of the sheet layers 14.

Preferably, the core section 16 includes at least two repeating units 22 of, in order, at least one of the unidirectional fabric layers 12 then at least one of the sheet layers 14. The repeating unit 22 may optionally comprise, in order, only one of the unidirectional fabric layers 12 and at least two of the sheet layers 14. The repeating unit 22 may alternatively or in addition include, in order, at least two of the woven fabric layers 12 and only one of the sheet layers 14. FIG. 2 shows an embodiment of the repeating unit 23 with a plurality of the unidirectional fabric layers stacked adjacent to a plurality of the sheet layers. Preferably, there are 3 to 50, more preferably 5 to 40, even more preferably 8 to 35, of the repeating units 22, 23.

As shown in FIG. 1, the core section 16 can have a sheet layer 14 at one end and a unidirectional fabric layer 12 at the other distal end. Alternatively, as shown in FIG. 3, the core section 24 can have a unidirectional fabric layer 12 at each end.

Referring again to FIG. 1, the core section 16 has a first strike end surface 30 and a second body facing end surface 32. Referring to FIG. 4, the article 40 can optionally further comprise a first strike section 42 and a body facing section 44. The first strike section 42 can comprise a plurality of the unidirectional fabric layers 12 stacked together and stacked on the first strike end surface 30 of the core section 16. The body facing section 44 can comprise a plurality of the unidirectional fabric layers 12 stacked together and stacked on the body facing surface 32 of the core section 16.

The first strike section 42 can have 2 to 30 unidirectional fabric layers stacked together and the body facing section 44 can have 2 to 30 unidirectional fabric layers stacked together. If desired the unidirectional fabric layers 12 of the first strike section 42 and the body facing section 44 can be the same or different.

Referring to FIG. 5, the core section 50 can comprises a plurality of core subsections 52, 54, each core subsection 52, 54 with a repeating unit 56.

Body Armor Article

Preferably, the article 10, 26, 40, 48 has a backface deformation of less than or equal to 44 mm at a projectile velocity (V_(o)) of 1430 ft/sec plus or minus (+/−) 30 ft/sec (436 m/sec+/−9 m/sec) in accordance with NIJ Standard—0101.06 “Ballistic Resistance of Body Armor”, issued in July, 2008.

Preferably, the unidirectional fabric layers 12 and the sheet layers 14 are only attached together at 10% or less of their surface areas allowing all or most of the remainder of the layers to move laterally and/or separate with respect to adjacent layers. The layers can be attached by stitches or adhesive or melt bonding, at edges and/or in the pattern of a cross (X), both as shown in FIG. 6, or in a pattern of squares typically done on a quilt, as shown in FIGS. 7 and 8. The stitch pattern illustrated in FIG. 7 is referred to as a quilted stitch pattern with additional edge stitching. More preferably, they are attached by less than 5%, and even more preferably less than 3%, of the surface area of the layers. Further, referring to FIG. 8, when the stitch pattern is in squares, preferably, the stitch spacing 60 is from about 48 to about 54 mm and more preferably from about 50 to about 52 mm. “Stitch spacing” is defined as the distance 60 between adjacent parallel stitches in a stitch pattern of squares on the face of layers. Also preferably the stitch length 62 is from about 3 to about 7 mm and more preferably from about 4 to about 6 mm. “Stitch length” is defined as the shortest repeating length 62 of stitching yarn that transverses the face of the layer.

By “unidirectional tape” is meant an array of generally parallel high tenacity multifilament yarns generally in a plane in a matrix resin. By “unidirectional assembly” is meant a plurality of the unidirectional tapes stacked with adjacent tapes with their yarns at angles inclined with respect to adjacent tapes. Typically the yarns in the tapes are at right angles with respect to yarns in adjacent tapes. Unidirectional tapes and assemblies are disclosed in U.S. Pat. No. 5,160,776 to Li et al.

Preferably, the unidirectional fabric layers 12 and the sheet layers 14, stacked together, have an areal density of 2.5 to 5.7 kg/m², and more preferably 3.0 to 5.2 kg/m².

Another embodiment of the invention may comprise auxiliary fabric layers on the anterior and posterior surfaces of the core section, the auxiliary fabric layers being free of adjacent sheet structures. The auxiliary fabric layers may be unidirectional or woven fabrics. Exemplary woven fabrics include plain, satin, basket, leno and twill weave styles. FIG. 9 shows generally at 70, a body armor article 71 comprising a core section 72, the core section comprising a plurality of alternating sequences 73 of a sheet structure and a unidirectional fabric layer. Auxiliary fabric layers are shown at 74 on the anterior and posterior surfaces of the core section.

INDUSTRIAL APPLICABILITY

The articles include protective apparel or body armor that protects body parts, such as vests, jackets, etc. from projectiles. The term “projectile” is used herein to mean a bullet or other object or fragment thereof, such as, fired from a gun.

Test Methods

The following test methods were used in the following Examples.

Temperature: All temperatures are measured in degrees Celsius (° C.).

Linear Density The linear density of a yarn or fiber is determined by weighing a known length of the yarn or fiber based on the procedures described in ASTM D1907-97 and D885-98. Decitex or “dtex” is defined as the weight, in grams, of 10,000 meters of the yarn or fiber. Denier (d) is 9/10 times the decitex (dtex).

Tensile Properties: The fibers to be tested were conditioned and then tensile tested based on the procedures described in ASTM D885-98. Tenacity (breaking tenacity), modulus of elasticity and elongation to break are determined by breaking test fibers on an Instron tester.

Areal Density The areal density of the fabric layer is determined by measuring the weight of each single layer of selected size, e.g., 10 cm×10 cm. The areal density of a composite structure is determined by the sum of the areal densities of the individual layers.

Average Acoustic Velocity: The acoustic velocity is the speed at which the tensile stress wave is transmitted through a material and was measured according to ASTM E494 in various directions and an average acoustic velocity was calculated. It is reported in m/sec. The reported average acoustic velocity is the average value of acoustic velocities that are measured traveling radially from a point of impact in the sheet layer set at (0,0) at 0°, 45°, 90°, 135°, 180°, −45°, −90°, −135° with respect to the positive x axis, with the machine or roll direction positioned along the x axis and the cross or transverse direction positioned along the y axis.

Ballistic Penetration and Backface Deformation Performance: Ballistic tests of the multi-layer panels are conducted in accordance with NIJ Standard—0101.06 “Ballistic Resistance of Body Armor”, issued in July, 2008. The smallest size of shoot pack, i.e. NIJ-C-1 size as disclosed in NIJ 0101.06, was selected for the test. A shot-to-edge distance of 3″ was used for the determination of backface deformation. The reported V50 values are average values for the number of shots fired for each example.

EXAMPLES

The following examples are given to illustrate the invention and should not be interpreted as limiting it in any way. All parts and percentages are by weight unless otherwise indicated. Examples prepared according to the process or processes of the current invention are indicated by numerical values. Control or Comparative Examples are indicated by letters. Data and test results relating to the Comparative and Inventive Examples are shown in Table 1.

Description of Layers

Layers of the following high tenacity fiber fabrics, unidirectional fabrics, and sheet structures were prepared and made into various composite assemblies for ballistic test as follows.

Fabric layer “F1” was a unidirectional fabric layer of ultra-high molecular weight polyethylene (or PE) available from Honeywell, Morristown, N.J. under the trade name of SA-3113. The unidirectional fabric layer had an areal weight of 96_gsm.

Fabric layer “F2” was a plain weave woven fabric of 600 denier (660 dtex) poly(p-pheynlene terephthalamide) (or PA) yarn available from E. I. du Pont de Nemours and Company under the trade name of Kevlar KM2® and was woven at 23×23 ends per inch (9.1×9.1 ends per centimeter). The woven fabric layer had an areal density of 124 gsm.

Sheet layer “S1” was a polyvinyl fluoride (or PVF) film or sheet structure available from E. I. DuPont de Nemours and Company under the trade name of Tedlar® with an average acoustic velocity of 1506 m/s, a thickness of 1.1 mil (0.030 mm), a ratio of maximum to minimum elongation at break for any two given directions of 1.3, and an areal density of 23.3 gsm.

Sheet layer “S2” was a polyethylene (or PE) nonwoven sheet structure flashspun from high-density polyethylene fibers, available from E. I. du Pont de Nemours and Company under the trade name of Tyvek® with an average acoustic velocity of 809 m/s, a thickness of 5.6 mil (0.140 mm), a ratio of maximum to minimum elongation at break for any two given directions of 1.92, and an areal density of 41 gsm.

Comparative Example A

In this example, a stacked article was made comprising thirty three layers of woven fabric layers F2. This article construction is referenced herein as 33F2. No unidirectional fabric layer was used in this article. The stacked article was made of the smallest C1 size template as defined in NIJ 0101.06 with each layer held together via a 2″ quilt stitch. The areal density of the article was about 4.09 kg/m². Ballistic tests were conducted using 0.357 magmum bullets based on the test protocol for NIJ Level II as described in NIJ standard—0101.06 entitled “Ballistic Resistance of Body Armor”. A shot-to-edge distance of 3″ was used for the determination of backface deformation. Results of the ballistic tests, including both V50 and backface deformation, as shown in Table 1, showed unacceptably high backface deformation, though its V50 performance is good.

Comparative Example B

In this example, a stacked article was made comprising forty two layers of unidirectional fabric layers F1. This article construction is referenced herein as 42F1. 100% unidirectional fabric layer was used in this article. The stacked article was made of the smallest C1 size template as defined in NIJ 0101.06 with each layer held together with stitches forming a perimeter stitch pattern only around the edge of the unidirectional fabric pack. The areal density of the article was about 4.03 kg/m². Ballistic tests were conducted using 0.357 magmum bullets based on the test protocol for NIJ Level II as described in NIJ standard—0101.06 entitled “Ballistic Resistance of Body Armor”. A shot-to-edge distance of 3″ was used for the determination of backface deformation. Results of the ballistic tests, including both V50 and backface deformation, as shown in Table 1, showed very good V50 with relatively low backface deformation as expected.

Example 1

In this example, a stacked article was made comprising, in order, a core section comprising a repeating unit of a unidirectional fabric layer F1 then a sheet layer S1, the unit repeated 33 times, and a further unidirectional fabric layer F1 with the latter layer facing the body side of the article. This article construction is referenced herein as 33(F1+S1)+1F1. The unidirectional fabric layers account for 80.9% of the total weight of the article. This stacked article was made of the smallest C1 size template as defined in NIJ 0101.06 with each layer held together with stitches forming a perimeter stitch pattern only around the edge of the unidirectional fabric pack. The areal density of the article was about 4.03 kg/m². Ballistic tests were conducted using 0.357 magnum bullets based on the test protocol for NIJ Level II as described in NIJ Standard—0101.06 entitled “Ballistic Resistance of Body Armor”. A shot-to-edge distance of 3″ was used for the determination of backface deformation. Results of the ballistic tests, including both V50 and backface deformation, as shown in the Table 1, showed good V50 with exceptionally low backface deformation values of 34 and 37 mm at 80.9% content of unidirectional fabric layers

Example 2

In this example, a stacked article was made comprising, a core section sandwiched by six layers of woven fabric (F2) on either side of the core section. The core section comprised a repeating unit of a sheet layer S2 then a unidirectional fabric layer F1, the unit repeated 19 times. This article construction is referenced herein as 6F2+19(F1+S1)+6F2. The unidirectional fabric layers account for only 44.6% of the weight of the total article. This stacked article was made of the smallest C1 size template as defined in NIJ 0101.06. The two woven fabric layers F2 were each held together with stitches forming a 2″ quilted stitch pattern The final assembly was then held together with stitches forming a perimeter stitch pattern only around the edge of the entire pack. The areal density of the article was about 4.09 kg/m². Ballistic tests were conducted using 0.357 magnum bullets based on the test protocol for NIJ Level II as described in NIJ Standard—0101.06 entitled “Ballistic Resistance of Body Armor”. A shot-to-edge distance of 3″ was used for the determination of backface deformation. Results of the ballistic tests, including both V50 and backface deformation, as shown in the Table 1, exhibit relatively low backface deformation values of 38 and 40 mm and good ballistic V50 of much higher than the requirement of reference velocity of 436 m/s, in spite of the relatively low content, i.e. 44.6%, of unidirectioinal fabric layers.

Examples 1 and 2 show that structures according to the present invention have substantially less backface deformation than those of the Comparative Examples A and B, though at a significant reduction in the content of unidirectional fabric layers.

TABLE 1 Areal Weight % of Density, V50 BFD Unidirectional Example Construction (kg/m²) (m/s) (mm) Fabric Layers 1 33 (F1 + S1) + 4.03 490 37; 34 80.9 1 F1 2 6 F2 + 19 4.09 471 38; 40 44.6 (F1 + S2) + 6 F2 Comparative 33 F2 4.09 508 44; 51 0.0 Example A Comparative 42 F1 4.03 530 37; 40 100.0 Example B 

What is claimed is:
 1. A body armor article for resisting ballistic objects, comprising: a plurality of unidirectional fabric layers made from yarns having a tenacity of at least 7.3 grams per dtex and a modulus of at least 100 grams per dtex; a plurality of sheet layers comprising non-woven random oriented fibrous sheets and/or non-fibrous films, each of the sheet layers having a thickness of at least 0.013 mm; the unidirectional fabric layers and the sheet layers stacked together comprising a first core section which includes at least two repeating units of, in order, at least one of the unidirectional fabric layers then at least one of the sheet layers; wherein (i) the sheet layers comprise 0.5 to 30 wt % of the total weight of the article, (ii) each of the sheet layers has an average acoustic velocity of at least 600 m/sec, (iii) the sheet layers are isotropic or substantially isotropic for average acoustic velocity, and (iv) the unidirectional fabric layers and the sheet layers are attached together at 10% or less of their surface areas.
 2. The article of claim 1, wherein the yarns have linear density of 50 to 4500 dtex, a tenacity of 10 to 65 g/dtex, a modulus of 150 to 2700 g/dtex, and an elongation to break of 1 to 8 percent.
 3. The article of claim 1, wherein the yarns are made of filaments made from a polymer selected from the group consisting of polyamides, polyolefins, polyazoles, and mixtures thereof.
 4. The article of claim 1, wherein each of the sheet layers have a thickness of no more than 0.152 mm.
 5. The article of claim 1, wherein the sheet layers are made of materials selected from the group consisting of polycondensation products of dicarboxylic acids with dihydroxyalcohols, ionomers, thermoplastic fluoropolymers, polyolefins, polyimides, aramid, glass, ceramic, carbon and mixtures thereof.
 6. The article of claim 1, wherein each of the sheet layers has a ratio of maximum strain to failure value to minimum strain to failure value of 1 to
 5. 7. The article of claim 1, wherein the core section includes 3 to 60 of the unidirectional fabric layers and 3 to 60 of the sheet layers.
 8. The article of claim 1, wherein there are 3 to 50 of the repeating units.
 9. The article of claim 1, wherein the core section has a first strike end surface and a body facing end surface; and the article further comprising a first strike section and a body facing section, the first strike section comprising a plurality of the unidirectional fabric layers stacked together and stacked on the first strike end surface of the core section, and the body facing section comprising a plurality of the unidirectional fabric layers stacked together and stacked on the body facing surface of the core section.
 10. The article of claim 1, wherein the core section has a unidirectional fabric end surface and a sheet end surface, further comprising at least one of the unidirectional fabric layers stacked on the sheet end surface of the core section.
 11. The article of claim 1, wherein the core section comprises a plurality of core subsections, each core subsection with a repeating unit.
 12. The article of claim 1, wherein the unidirectional fabric layers and the sheet layers are only attached together at 10% or less of their surface areas allowing all or most of the remainder of the layers to move laterally and/or separate with respect to adjacent layers.
 13. The article of claim 1, wherein the unidirectional fabric layers and the sheet layers, stacked together, have an areal density of 2.5 to 5.7 kg/m².
 14. The article of claim 9, wherein the first strike section has 2 to 30 unidirectional fabric layers stacked together and the body facing section has 2 to 30 unidirectional fabric layers stacked together. 